In recent years, exhaustive proteome analysis has progressed on a worldwide scale, and searches for disease markers using the proteome analysis have widely taken place (Patent Literatures 1 to 2 and Non Patent Literatures 1 to 3). In the proteome analysis, generally, a protein contained in a sample of biological origin or a peptide as its degradation product is isolated; the amino acid sequence of the isolated protein or peptide is analyzed using a mass spectrometer; the resultant amino acid sequence is compared with amino acid sequences in a database; and thereby the protein or the peptide contained in the sample is identified. Because proteins expressed in vivo differ by the presence or absence of disease, the protein or the peptide found to increase or decrease in expression level in a disease-specific manner by the proteome analysis has potential to be able to be used as a marker for the disease.
Through the proteome analysis, the present inventors identified the 5.9 kDa peptide as one of new serum peptides increasing or decreasing with the habit of drinking from serum samples collected with time from an alcoholic patient hospitalized for the purpose of abstinence and found that this can be used as a diagnosis marker for hepatic disease (Patent Literature 1 and Non Patent Literatures 1 to 2).
The present inventors showed that two monoclonal antibodies obtained using the MI-length 5.9 kDa peptide consisting of 54 residues as an antigen can be used to perform the immunoassay of the isolated 5.9 kDa peptide (Patent Literature 1).